This application pertains to the art of overtravel indicators and, more particularly, to such indicators for indicating overtravel of a piston. The invention is particularly applicable for use with pressure converters used on vehicles for converting pneumatic pressure to hydraulic pressure. However, it will be appreciated that the improved indicator can be used with other devices.
Overtravel indicators of known types include those disclosed in U.S. Pat. Nos. 444,077 issued Jan. 6, 1891, to Thompson et al.; 3,772,672 issued Nov. 13, 1973, to Adahan; and 3,782,780 issued Jan. 1, 1974, to Orzel.
The Thompson indicator comprises an elongated rod mounted for axial movement in one end of a cylinder and having a rod inner end located within the cylinder for being acted upon by a piston to project the rod outwardly of the cylinder and indicate how far the piston has moved. The Thompson indicator does not provide a warning for the operator of a vehicle or the like when failure is imminent or has occurred. The air brake cylinder in Thompson is normally mounted in a location on the vehicle where it is not visible to the operator and is actually used by a mechanic for adjusting the brake system. The Adahan and Orzel devices provide an electrical signal to warn the operator of a vehicle that a failure is imminent or has occurred. In these devices, safety requires that the vehicle be shut down when the signal occurs and there is no way of telling whether a complete failure has occurred or whether there is simply wear requiring adjustments.
It would be desirable to have an indicator which would provide a signal indicating when a failure is imminent or has occurred, and providing another signal indicating the degree of failure.